USDA-ARSUSDA-ARS

• Crop ET

• PET Networks

• How to obtain & use information from the internet

• Crop ET

• PET Networks

• How to obtain & use information from the internet

Irrigation TechnicalTraining

Irrigation TechnicalTraining

Texas SWCSKerrville, TexasJune 16, 1999

Texas SWCSKerrville, TexasJune 16, 1999

IRRIGATIONSCHEDULINGIRRIGATION

SCHEDULING

Irrigation SchedulingIrrigation

Scheduling• Soil water balance

– soil / plant / atmosphere / water

• Irrigation system dynamics– efficiency / uniformity

• Metering (control & feedback)– irrigation water / soil water / crop water

• Soil water balance– soil / plant / atmosphere / water

• Irrigation system dynamics– efficiency / uniformity

• Metering (control & feedback)– irrigation water / soil water / crop water

Crop ETCrop ETSoil Water Balance

Si = Si-1 + (P - Q) + (I - Q) - D - ET

Si = “root zone” soil water on day i

(P - Q) = “effective” precipitation

(I - Q) = “effective” (net) irrigation

D = percolation beneath the root zone

ET = evaporation plus transpiration

Soil Water Balance

Si = Si-1 + (P - Q) + (I - Q) - D - ET

Si = “root zone” soil water on day i

(P - Q) = “effective” precipitation

(I - Q) = “effective” (net) irrigation

D = percolation beneath the root zone

ET = evaporation plus transpiration

Soil Water Balance

use inputs losses

ET = SW + (I + P) - (D + Q)

Some percolation (D) may be required for salinity leaching but can contain nutrients and agro-chemicals that are not desirable for the environment.

Soil Water Balance

use inputs losses

ET = SW + (I + P) - (D + Q)

Some percolation (D) may be required for salinity leaching but can contain nutrients and agro-chemicals that are not desirable for the environment.

Crop ETCrop ET

Soil WaterSoil Water• Spatial variability

– crop– soil chemical properties

• salinity• fertility

– soil physical properties• infiltration & percolation• plant available soil water

• Spatial variability– crop– soil chemical properties

• salinity• fertility

– soil physical properties• infiltration & percolation• plant available soil water

Soil WaterSoil Water• Spatial variability (cont.)

– precipitation• runoff & run-on

– irrigation• runoff & run-on• hydraulics / operation dynamics

• Spatial variability (cont.)– precipitation

• runoff & run-on

– irrigation• runoff & run-on• hydraulics / operation dynamics

EvapotranspirationEvapotranspiration

• ET = E + TE = evaporation

T = transpiration

E can depend on irrigation method and wetting frequency

T is strongly correlated to crop dry matter

• ET = E + TE = evaporation

T = transpiration

E can depend on irrigation method and wetting frequency

T is strongly correlated to crop dry matter

Maximum ET Maximum ET

• Potential Evapotranspiration (PET)– basically goes back to Penman (1948)

– not in “vogue” today, except in Texas

– implies zero “bulk” surface resistance• wet crop• water surfaces

• Potential Evapotranspiration (PET)– basically goes back to Penman (1948)

– not in “vogue” today, except in Texas

– implies zero “bulk” surface resistance• wet crop• water surfaces

Reference Evapotranspiration

Reference Evapotranspiration

• Applies to a specific crop– short grass (0.08 to 0.15 m tall; usually a cool-

season type species like fescue, ryegrass, or bluegrass that doesn’t grow in most parts of Texas) … ETo

– tall (>0.5 m tall) alfalfa (again, not a major crop in Texas) … ETr

– well-watered (not deficient in soil water)

• Applies to a specific crop– short grass (0.08 to 0.15 m tall; usually a cool-

season type species like fescue, ryegrass, or bluegrass that doesn’t grow in most parts of Texas) … ETo

– tall (>0.5 m tall) alfalfa (again, not a major crop in Texas) … ETr

– well-watered (not deficient in soil water)

Penman EquationPenman Equation

Wf = 6.43 (1 + 0.53 u2) … for short grasssource Penman (1948)

(Rn - G) + Wf (es - ea)ETo =

( + )

ParametersParameters

= des/T = f (air temperature)

[e*(T0) - e*(Ta)] / (T0 - Ta)

(barometric pressure or elevation)

• (es - ea) = VPD = [es(Ta)] (1 - RH)

= des/T = f (air temperature)

[e*(T0) - e*(Ta)] / (T0 - Ta)

(barometric pressure or elevation)

• (es - ea) = VPD = [es(Ta)] (1 - RH)

Modified Penman Equation

Modified Penman Equation

• the wind function (Wf) is “fitted”• may vary on how VPD is computed• might apply to grass or alfalfa base

depending on Rn and Wf

e.g., FAO-24 Penman equation for grass

• the wind function (Wf) is “fitted”• may vary on how VPD is computed• might apply to grass or alfalfa base

depending on Rn and Wf

e.g., FAO-24 Penman equation for grass

Penman-Monteith Equation

Penman-Monteith Equation

• source Monteith (1965)

rs = “bulk” surface resistance

.... 70 s/m for grass

.... 45 s/m for alfalfa

ra = aerodynamic resistance K / u2

• source Monteith (1965)

rs = “bulk” surface resistance

.... 70 s/m for grass

.... 45 s/m for alfalfa

ra = aerodynamic resistance K / u2

(Rn - G) + 86.4 Cp (es - ea) / raETo = [ + (1 + rs/ra)

FAO-56 PM Equation

FAO-56 PM Equation

• source Allen et al. (1998)

a slight simplification of the Penman-

Monteith equation.

• source Allen et al. (1998)

a slight simplification of the Penman-

Monteith equation.

0.408 (Rn - G) + u2 (es - ea)

ETo = + (1 + 0.34 u2)

900

T + 273

Important ResourcesImportant Resources

19901993 1998

PETPET

• Most often in Texas, due to prior history and use, PET (potential evapotranspiration) is computed for a “grass reference” crop assuming many if not all the concepts in ASCE Manual No. 70, SCS (NRCS) Chapter 2, TWDB-98, or FAO-56.

• Most often in Texas, due to prior history and use, PET (potential evapotranspiration) is computed for a “grass reference” crop assuming many if not all the concepts in ASCE Manual No. 70, SCS (NRCS) Chapter 2, TWDB-98, or FAO-56.

Crop CoefficientsCrop Coefficients

• Single Kc approach

ETc = Kco ETo (grass) or

ETc = Kcr ETr (alfalfa)

The “interchangeability” of Kc values

depends on the ETo / ETr ratio or

function.

• Single Kc approach

ETc = Kco ETo (grass) or

ETc = Kcr ETr (alfalfa)

The “interchangeability” of Kc values

depends on the ETo / ETr ratio or

function.

Crop CoefficientsCrop Coefficients

• Dual crop coefficient approach

ETc = (Kcbo + Ke) ETo

ETc = (Kcbr + Ke) ETr

Kcbo or cbr = “basal” Kco or cr (“dry” soil surface BUT “well-watered” crop )

Ke = soil water evaporation coefficient

• Dual crop coefficient approach

ETc = (Kcbo + Ke) ETo

ETc = (Kcbr + Ke) ETr

Kcbo or cbr = “basal” Kco or cr (“dry” soil surface BUT “well-watered” crop )

Ke = soil water evaporation coefficient

Deficit Soil WaterDeficit Soil Water

• Single Kc approach

ETcadj = (Ks Kco) ETo

ETcadj = (Ks Kcr) ETr

• Dual Kc approach

ETcadj = (Ks Kcbo + Ke) ETo

ETcadj = (Ks Kcbr + Ke) ETr

• Single Kc approach

ETcadj = (Ks Kco) ETo

ETcadj = (Ks Kcr) ETr

• Dual Kc approach

ETcadj = (Ks Kcbo + Ke) ETo

ETcadj = (Ks Kcbr + Ke) ETr

PET NetworksPET Networks

• Provide “uniform” regional coverage with data to guide irrigation decision making

• Educate irrigators and the public about irrigation water needs

• Regional climate and weather data resource

• Provide “uniform” regional coverage with data to guide irrigation decision making

• Educate irrigators and the public about irrigation water needs

• Regional climate and weather data resource

OklahomaMesonet

TexasMesonet

TxPET NetworkSouth Plains (Lubbock)North Plains (Amarillo)TAMU Network (CS)[ Coastal Bend (CC) ]

NP-PET Sites

- PET Sites

> 1,200 mi. for a circuit trip

FarwellDimmitt

Earth

BushlandWhite DeerWellington

DalhartEtter

MorsePerryton

Grass ET Measurement

Grass ET Measurement

• Weighing lysimeter

• 5 ft by 5 ft by 8 ft deep

• Pullman clay loam monolith

• SDI irrigated

• Weighing lysimeter

• 5 ft by 5 ft by 8 ft deep

• Pullman clay loam monolith

• SDI irrigated

Lysimeter ET, mm d-10 2 4 6 8 10 12 14

Co

mp

ute

d E

To

, mm

d-1

0

2

4

6

8

10

12

14

161995199619971998Regression1:1 Line

April throughOctober

ETo = 1.16 + 0.85*ETlys

r2 = 0.728

Measuring Crop ETMeasuring Crop ETInside view of weighinglysimeter

3 m1995 SoybeanCrop

0

2

4

6

8

10

12

14

16

18 S

oyb

ean

ET, m

m/d

0

100

200

300

400

500

600

700

800

Cu

mu

lati

ve E

T, m

m

120 140 160 180 200 220 240 260 280 Day of Year - 1995

1995 Soybean ET

MeanSW LysimeterNW Lysimeter

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

Mean

Kc (

ET

/ P

ET

)

05/01 05/31 06/30 07/30 08/29 09/28 10/28 Date 1995

Mean Kc Kc Reg (n5)

Soybean Crop Coefficient

Pl Em v2 v3 v4 v5 r2 r3 r4 r5 r6 r7 Pm Hv

Crop InformationCrop Information• Crops

– corn, sorghum, wheat, cotton, soybean, peanut

• Sowing Dates– 4 dates that bracket typical practices

• Hybrids / Varieties / Cultivars– full-season and short-season for

sorghum and corn

• Crops– corn, sorghum, wheat, cotton, soybean,

peanut

• Sowing Dates– 4 dates that bracket typical practices

• Hybrids / Varieties / Cultivars– full-season and short-season for

sorghum and corn

NP-PET InformationNP-PET Information

• “Well-watered” crops

• “Normal” crops without diseases or pest problems

• Daily, 3-day, 7-day, seasonal ET rates

• Predicted crop development stage for each crop (& hybrid type) and sowing date

• “Well-watered” crops

• “Normal” crops without diseases or pest problems

• Daily, 3-day, 7-day, seasonal ET rates

• Predicted crop development stage for each crop (& hybrid type) and sowing date

NP-PET Information ...

NP-PET Information ...

• Daily GDDs and GDD sums for each crop (& hybrid type) and sowing date

• 3-day climate summary– rainfall, air temperature, soil

temperatures, and PET

• Alerts and messages (regional pest information, news, upcoming events)

• Daily GDDs and GDD sums for each crop (& hybrid type) and sowing date

• 3-day climate summary– rainfall, air temperature, soil

temperatures, and PET

• Alerts and messages (regional pest information, news, upcoming events)

NP-PET UsersNP-PET Users• Growers / Irrigators / Farm Managers• Production Consultants & Advisors• Agricultural Industries• Agronomists / Agricultural Engineers• Researchers• Extension Personnel• Water District & Regulatory Personnel• Design Personnel & Consultants• Meteorologists / Climatologists

• Growers / Irrigators / Farm Managers• Production Consultants & Advisors• Agricultural Industries• Agronomists / Agricultural Engineers• Researchers• Extension Personnel• Water District & Regulatory Personnel• Design Personnel & Consultants• Meteorologists / Climatologists

NP-PET GoalsNP-PET Goals

• Provide accessible “generalized” data of consistent quality and reliability

• Provide wide-area data for private consultants and crop advisors in near “real-time” so that tailored client products can be developed

• Provide accessible “generalized” data of consistent quality and reliability

• Provide wide-area data for private consultants and crop advisors in near “real-time” so that tailored client products can be developed

How is the NP-PET Information

Disseminated ?

How is the NP-PET Information

Disseminated ?• Daily fax to subscribers (350+ per night)

• Internet Web site

• Daily fax to subscribers (350+ per night)

• Internet Web site

Fax RecipientsFax Recipients

• Subscribed Growers / Irrigators

• Crop Consultants

• Local Cooperatives

• Newspapers

• News Stations: Radio & TV

• Subscribed Growers / Irrigators

• Crop Consultants

• Local Cooperatives

• Newspapers

• News Stations: Radio & TV

WWW UsersWWW Users

• Production Personnel - (own models)

• Consultants - (own models)

• Researchers / Modelers - (water, insect, disease, air, dust modeling development)

• Extension Personnel

• Texas Mesonet (possibility ??)

• Production Personnel - (own models)

• Consultants - (own models)

• Researchers / Modelers - (water, insect, disease, air, dust modeling development)

• Extension Personnel

• Texas Mesonet (possibility ??)

Grass ET EstimatesGrass ET Estimates

• PET data are useful for estimating urban lawn water needs– TAEX Master Gardener Program

– Water Smart Program

• Municipal / Schools / Golf Course irrigation decisions

• PET data are useful for estimating urban lawn water needs– TAEX Master Gardener Program

– Water Smart Program

• Municipal / Schools / Golf Course irrigation decisions

Fax Output of 09/08/96, Etter,TX - (upper left)

Fax Output of 09/08/96, Etter,TX - (upper left)

North Plains PET Network Weather Station, Etter, TX

TemperaturesDate PET ---AIR--- ---Soil-- Prec.

in. Max Min 2 in 6 in in09/05/96 0.20 84 61 70 71 0.0009/06/96 0.18 84 62 69 70 0.1909/07/96 0.13 77 61 68 69 0.03Ten Day Average 69 70

CORN Short Season VarietySeed Acc Grwth Day 3 day 7 day SeasDate GDD Stage -----in/day----- in.

04/01 3148 Harvest 0.00 0.00 0.00 29.504/15 3004 Harvest 0.00 0.00 0.00 28.005/01 2810 Blk lyr 0.09 0.12 0.13 26.305/15 2566 ½ mat 0.12 0.15 0.17 23.4

Fax Output of

09/08/1996- Etter, TX - (upper right)

Fax Output of

09/08/1996- Etter, TX - (upper right)

North Plains PET Network Weather Station, Etter, TX

Date -----Growing Degree Days-----Crn Srg Pnt Cot Soy Bet Wheat

09/05/96 22 22 17 12 26 32 3809/06/96 23 23 18 13 27 33 3909/07/96 19 19 14 9 23 29 37

CORN Long Season VarietySeed Grwth Day 3 day 7 day Seas.Date Stage -----in/day----- in.

04/01 Harvest 0.00 0.00 0.00 32.204/15 Harvest 0.00 0.09 0.14 30.805/01 Blk lyr 0.12 0.16 0.18 27.805/15 ½ mat 0.16 0.20 0.22 24.2

How do you use the information ?

How do you use the information ?

• Rainfall data– field basis

• Irrigation data– field applications

• Rainfall data– field basis

• Irrigation data– field applications

Requires training, requires experience, and requires some local data (rainfall, irrigation, cropping information .....)

How do you use the information ? ...

How do you use the information ? ...

• System capacity — gpm/ac or in./d or an estimate of ‘application efficiency’

• Crop data – Planting date

– Type of hybrid for corn or sorghum

• System capacity — gpm/ac or in./d or an estimate of ‘application efficiency’

• Crop data – Planting date

– Type of hybrid for corn or sorghum

0

0.1

0.2

0.3

0.4

0.5

0.6 D

aily E

T, in

./d

0

5

10

15

20

25

30

35

Cu

m. R

ain

or E

T, in

.

120 140 160 180 200 220 240 260 280 Day of Year - 1995

1995 Soybean

Cum ET

Cum. Rain

Mean ET

}

6 gpm/ac

1.2 in. @ 6 gpm/ac

5 gpm/ac

1.8 in. @ 5 gpm/ac

4 gpm/ac

2.6 in. @ 4 gpm/ac

What Value is the PET Information ?What Value is the PET Information ?

• Provides useful regional information– rainfall

– soil temperatures (planting guides)

– data are being used in pest models

– quantifies water needs

– indicates crop development rates

• Provides useful regional information– rainfall

– soil temperatures (planting guides)

– data are being used in pest models

– quantifies water needs

– indicates crop development rates

What Value is the PET

Information ? ...

What Value is the PET

Information ? ...• Water savings

– could reduce pumping costs by $2-5,000 for a 1,000 ac irrigated farm by saving only 1 inch of water

• Avoid uncertainties in climatic damages– late spring freezes on wheat

• Water savings– could reduce pumping costs by $2-5,000

for a 1,000 ac irrigated farm by saving only 1 inch of water

• Avoid uncertainties in climatic damages– late spring freezes on wheat

What Value is the PET

Information ? ...

What Value is the PET

Information ? ...• LOOK at the PET data as a valued “new

tool” or accessory– keep maintaining accurate records

– keep doing plant and soil water sampling

– keep monitoring irrigation system performance

• LOOK at the PET data as a valued “new tool” or accessory– keep maintaining accurate records

– keep doing plant and soil water sampling

– keep monitoring irrigation system performance

PET ToolsPET Tools

• Can be used as a periodic guide post (twice a week or so) to see if you are applying enough water

• Provides crop consultants uniform data that they can utilize for customer portfolios

• Can be used as a periodic guide post (twice a week or so) to see if you are applying enough water

• Provides crop consultants uniform data that they can utilize for customer portfolios

NP PET Webhttp://amarillo2.tamu.edu/nppet/petnet1.

htm

NP PET Webhttp://amarillo2.tamu.edu/nppet/petnet1.

htm

Data:by station10-current9 archivedfax pageshourly data

SP (Lubbock) PEThttp://achilleus.tamu.edu/

SP (Lubbock) PEThttp://achilleus.tamu.edu/

Lubbock, Lamesa,& HalfwayCurrent PET & GDDArchived data:Lubbock since 1994Lamesa since 1996Halfway since 1996

Texas Evaporanspirati

onWeb Site

http://www.agen.tamu.edu/wqit/petnet/

Texas Evaporanspirati

onWeb Site

http://www.agen.tamu.edu/wqit/petnet/20 stations

some with databack to late 1996.Interactive wateruse calculator,Kc data, etc.

Other ExamplesOther ExamplesHigh PlainsClimate CenterUniv. of Nebr.http://hpccsun.unl.edu/

Models / Data SitesModels / Data Sites• New Mexico State Climate Center

– http://weather.nmsu.edu/

• ET Models (Silsoe College in England)– http://spider.silsoe.cranfield.ac.uk/mig/

SilsoeModels.htm

• SWIM v2 (CSIRO Australia)– http://www.clw.csiro.au/products/swim/

index.htm

• New Mexico State Climate Center– http://weather.nmsu.edu/

• ET Models (Silsoe College in England)– http://spider.silsoe.cranfield.ac.uk/mig/

SilsoeModels.htm

• SWIM v2 (CSIRO Australia)– http://www.clw.csiro.au/products/swim/

index.htm

ET ResourcesET Resources“Evapotranspiration and IrrigationWater Requirements”M. E. Jensen, R. G. Allen, and R. D.Burman

(ASCE Manuals and Reports onEngineering Practice No. 70)ISBN: 0-87262-763-2Published: 1990, American Society ofCivil EngineersList $72.00 / Members $54.00American Society of Civil Engineers1801 Alexander Bell DriveReston, VA 20191-44001-800-548-2723 or 1-703-295-6300http://www.pubs.asce.org

“Irrigation Water Requirements”D.L. Martin and J.R. Gilley

(Chapter 2, Part 623, NationalEngineering Handbook)Published: September 1993USDA-NRCSNEH-623-2Consolidated Forms and Publ.Distribution Center3222 Hubbard Rd.Landover, MD 20785

The EndThe EndUSDA-Agricultural Research Service

in cooperation with the

Texas Agricultural Experiment Station

and the Texas Agricultural Extension Service

serving the U.S. and Texas

so we can have food and fiber forever!

USDA-Agricultural Research Service

in cooperation with the

Texas Agricultural Experiment Station

and the Texas Agricultural Extension Service

serving the U.S. and Texas

so we can have food and fiber forever!